includes() JavaScript Array Method – How to Check If an Array Includes an Item

Whenever you use includes() on an array, the method does the following:

1. It checks if the calling array includes the method’s first argument.
2. It returns true if the array includes the argument. Otherwise, it returns false.

Note

• A calling array is an array on which you used includes(). So, in bestColorsList.includes("white"), bestColorsList is the calling array.
• includes() is sometimes written as Array.prototype.includes() because it is a method of the Array object’s prototype property.

Syntax of the includes() Method

includes() accepts two arguments. Here is the syntax:

callingArray.includes(valueToFind, startIndex);

Note

The includes() method is case-sensitive.

Argument 1: valueToFind

A valueToFind is the first argument accepted by the includes() method. It defines the value you wish to find in the calling array.

Example 1: Check if a given array includes "Tuesday"

["Sunday", "Tuesday", "Friday"].includes("Tuesday");

// The invocation above will return: true

Try Editing It

Example 2: Check if a given array includes "SunDay"

["Sunday", "Tuesday", "Friday"].includes("SunDay");

// The invocation above will return: false

Try Editing It

The snippet above returned false because the includes() method is case-sensitive.

Example 3: Check if a given array includes 5

[1, 3, 5, 7].includes(5);

// The invocation above will return: true

Try Editing It

Argument 2: startIndex

The startIndex argument is optional. It specifies the index position where you want the computer to start searching for the valueToFind argument.

Note

The startIndex argument’s default value is 0. Therefore, if omitted, the search will begin at index 0.

Example 1: From the 3rd index position, check if a given array includes "Tuesday"

const daysOfWeek = [
  "Sunday",
  "Tuesday",
  "Thursday",
  "Friday",
  "Tuesday",
  "Sunday",
  "Tuesday",
  "Friday",
];

daysOfWeek.includes("Tuesday", 3);

// The invocation above will return: true

Try Editing It

Example 2: From the 1st index position, check if a given array includes "Sunday"

const daysOfWeek = [
  "Sunday",
  "Tuesday",
  "Friday",
  "Monday",
  "Tuesday",
  "Friday",
];

daysOfWeek.includes("Sunday", 1);

// The invocation above will return: false

Try Editing It

Tip

• To find the index position of an item within an array, use indexOf().
• You can also use includes() on a string.